docs: def validateFunction(strFunc, netParamsVars):
      ''' returns True if "strFunc" can be evaluated'''
      from math import exp, log, sqrt, sin, cos, tan, asin, acos, atan, sinh, cosh, tanh, pi, e
      rand = h.Random()
      stringFuncRandMethods = ['binomial', 'discunif', 'erlang', 'geometric', 'hypergeo', 
          'lognormal', 'negexp', 'normal', 'poisson', 'uniform', 'weibull']
      
      for randmeth in stringFuncRandMethods: strFunc = strFunc.replace(randmeth, 'rand.'+randmeth)
      
      variables = {
          "pre_x"  : 1, "pre_y"  : 1, "pre_z"  : 1,
          "post_x" : 1, "post_y" : 1, "post_z" : 1, 
          "dist_x" : 1, "dist_y" : 1, "dist_z" : 1,
          "pre_xnorm"  : 1, "pre_ynorm"   : 1, "pre_znorm"  : 1,
          "post_xnorm" : 1, "post_ynorm"  : 1, "post_znorm" : 1,
          "dist_xnorm" : 1, "dist_ynorm"  : 1, "dist_znorm" : 1,
          "dist_3D"    : 1, "dist_3D_border" : 1, "dist_2D" : 1,
          "dist_norm3D": 1, "dist_norm2D" : 1, "rand": rand,
          "exp": exp, "log":log, "sqrt": sqrt,
          "sin":sin, "cos":cos, "tan":tan, "asin":asin, 
          "acos":acos, "atan":atan, "sinh":sinh, "cosh":cosh, 
          "tanh":tanh, "pi":pi,"e": e
      }
      
      # add netParams variables
      for k, v in netParamsVars.items():
          if isinstance(v, Number):
              variables[k] = v
  
      try: 
          eval(strFunc, variables)
          return True
      except:
          return False